Polymers are used at water treatment facilities for liquid/solid separation processes as an aid in the removal of undesired particles from water and wastewater. These concentrated liquid (emulsion and dispersion) polymers require dilution and activation at the water treatment facility prior to being introduced into the process stream. Owing to the nature of the polymer molecule, the dilution and activation processes must be carried out under carefully controlled conditions in order to assure optimum performance of the polymer.
The polymer is present in the emulsion in the form of microscopic gel particles consisting of thousands of individual long chain polymer molecules which are tightly intertwined and entangled with one another. Within milliseconds of the gel particle making contact with diluting water, the water begins to dissolve the polymer by penetrating into the particle, and activate the entangled molecules by loosening and extending them, swelling the polymer to many times its original size. As the water penetrates the particle, the molecules or section of molecules at the outside layer of the particle are only partially dissolved and become sticky. If particles in a similar condition are allowed to come into contact at this stage if dissolution, they will agglomerate into clumps which can range into macroscopic sizes. Once this happens the effective area to volume ratio of the clumps decreases and slows down dissolution greatly. These agglomerations must either be broken up by agitation so dissolution can be accomplished in a rapid manner, or a substantially longer time must be allowed for the polymer to dissolve, a technique referred to as aging. When additional agitation is applied, those molecules which are at or near the surface of the agglomerated particle will go into solution first. Once they are dissolved and fully extended they become fragile and are subject to being broken into shorter lengths, thereby decreasing their effectiveness. If aging is relied upon to complete dissolution, the time required will dictate very much larger mixing/aging vessels to achieve the necessary throughput for a given process. Accordingly, there is a need for methods and apparatus for preventing gel clumps or aggregates from forming in the dilution and activation processes.
Polymer agglomeration can be reduced or eliminated by subjecting the diluted polymer solution to relatively high shear forces, which can be obtained using a centrifugal impeller in a mixing chamber. A centrifugal impeller is a disk-shaped device which rotates, drawing solution into the impeller at the axis of rotation, and forcing it out at the outer edges under centrifugal force, through internal channels in the impeller. However, in some such apparatus the polymer is placed in the mixing chamber adjacent the outer edge of the chamber or impeller, where the shear forces are relatively low and not in immediate contact with fresh dilutant. This does not provide optimum conditions for discouraging agglomeration. In other such apparatus, the polymer and dilution water are placed in solution at least several seconds prior to entering the impeller chamber, which also does not produce optimum conditions for discouraging agglomeration. Thus, there is a need for polymer mixing and activation apparatus which minimizes polymer agglomeration and discourages gel aggregates from forming.
Accordingly, one object of this invention is to provide new and improved apparatus for dissolving and activating polymer emulsions in dilution water.
Another object is to provide new and improved apparatus for discouraging agglomeration of polymer molecules when mixed with dilution water.